In order to extract a pile from the ground, it is desirable to accompany a traction force applied to the pile with percussions facilitating the removal of the pile. Similarly, in driving a pile into the ground the best results can be obtained when the energy of percussion transmitted to a pile consists of two components one of which provides vibrations while another forces the pile into the ground.
Various mechanical, hydraulic and pneumatic instruments have been designed to this end. Mechanical equipment is rather complex and ordinarily is subjected to much damage. On the other hand, fluid-pressure apparatus can hardly be operated when ambient temperature becomes very low.
My U.S. Pat. No. 4,215,297 describes an electromagnetic percussion appliance wherein a reciprocable non-magnetic ram is coupled with an armature of an electromagnetic coil constituting an electromagnetic hammer adapted mostly for one-directional operation.
Two-directional conventional implements adapted both for driving and for extracting operations, in many instances, have to be reassembled or turned upside-down on changeable supports, in order to switch them from one operation to another.